| 1. |
- Abbott, Benjamin W., et al.
(författare)
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Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire : an expert assessment
- 2016
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 11:3
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Tidskriftsartikel (refereegranskat)abstract
- As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.
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| 2. |
- Alfredsson, Hanna, et al.
(författare)
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Amorphous silica pools in permafrost soils of the Central Canadian Arctic and the potential impact of climate change
- 2015
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 124:1-3, s. 441-459
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the distribution, storage and landscape partitioning of soil amorphous silica (ASi) in a central Canadian region dominated by tundra and peatlands to provide a first estimate of the amount of ASi stored in Arctic permafrost ecosystems. We hypothesize that, similar to soil organic matter, Arctic soils store large amounts of ASi which may be affected by projected climate changes and associated changes in permafrost regimes. Average soil ASi storage (top 1 m) ranged between 9600 and 83,500 kg SiO2 ha(-1) among different land-cover types. Lichen tundra contained the lowest amounts of ASi while no significant differences were found in ASi storage among other land-cover types. Clear differences were observed between ASi storage allocated into the top organic versus the mineral horizon of soils. Bog peatlands, fen peatlands and wet shrub tundra stored between 7090 and 45,400 kg SiO2 ha(-1) in the top organic horizon, while the corresponding storage in lichen tundra, moist shrub- and dry shrub tundra only amounted to 1500-1760 kg SiO2 ha(-1). Diatoms and phytoliths are important components of ASi storage in the top organic horizon of peatlands and shrub tundra systems, while it appears to be a negligible component of ASi storage in the mineral horizon of shrub tundra classes. ASi concentrations decrease with depth in the soil profile for fen peatlands and all shrub tundra classes, suggesting recycling of ASi, whereas bog peatlands appeared to act as sinks retaining stored ASi on millennial time scales. Our results provide a conceptual framework to assess the potential effects of climate change impacts on terrestrial Si cycling in the Arctic. We believe that ASi stored in peatlands are particularly sensitive to climate change, because a larger fraction of the ASi pool is stored in perennially frozen ground compared to shrub tundra systems. A likely outcome of climate warming and permafrost thaw could be mobilization of previously frozen ASi, altered soil storage of biogenically derived ASi and an increased Si flux to the Arctic Ocean.
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| 3. |
- Alfredsson, H., et al.
(författare)
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Estimated storage of amorphous silica in soils of the circum-Arctic tundra region
- 2016
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 30:3, s. 479-500
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the vertical distribution, storage, landscape partitioning, and spatial variability of soil amorphous silica (ASi) at four different sites underlain by continuous permafrost and representative of mountainous and lowland tundra, in the circum-Arctic region. Based on a larger set of data, we present the first estimate of the ASi soil reservoir (0-1 m depth) in circum-Arctic tundra terrain. At all sites, the vertical distribution of ASi concentrations followed the pattern of either (1) declining concentrations with depth (most common) or (2) increasing/maximum concentrations with depth. Our results suggest that a set of processes, including biological control, solifluction and other slope processes, cryoturbation, and formation of inorganic precipitates influence vertical distributions of ASi in permafrost terrain, with the capacity to retain stored ASi on millennial timescales. At the four study sites, areal ASi storage (0-1 m) is generally higher in graminoid tundra compared to wetlands. Our circum-Arctic upscaling estimates, based on both vegetation and soil classification separately, suggest a storage amounting to 219 ± 28 and 274 ± 33 Tmol Si, respectively, of which at least 30% is stored in permafrost. This estimate would account for about 3% of the global soil ASi storage while occupying an equal portion of the global land area. This result does not support the hypothesis that the circum-Arctic tundra soil ASi reservoir contains relatively higher amounts of ASi than other biomes globally as demonstrated for carbon. Nevertheless, climate warming has the potential to significantly alter ASi storage and terrestrial Si cycling in the Arctic.
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| 4. |
- Bartsch, Annett, et al.
(författare)
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Can C-band synthetic aperture radar be used to estimate soil organic carbon storage in tundra?
- 2016
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 13:19, s. 5453-5470
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Tidskriftsartikel (refereegranskat)abstract
- A new approach for the estimation of soil organic carbon (SOC) pools north of the tree line has been developed based on synthetic aperture radar (SAR; ENVISAT Advanced SAR Global Monitoring mode) data. SOC values are directly determined from backscatter values instead of upscaling using land cover or soil classes. The multi-mode capability of SAR allows application across scales. It can be shown that measurements in C band under frozen conditions represent vegetation and surface structure properties which relate to soil properties, specifically SOC. It is estimated that at least 29 Pg C is stored in the upper 30 cm of soils north of the tree line. This is approximately 25% less than stocks derived from the soil-map-based Northern Circumpolar Soil Carbon Database (NCSCD). The total stored carbon is underestimated since the established empirical relationship is not valid for peatlands or strongly cryoturbated soils. The approach does, however, provide the first spatially consistent account of soil organic carbon across the Arctic. Furthermore, it could be shown that values obtained from 1 km resolution SAR correspond to accounts based on a high spatial resolution (2 m) land cover map over a study area of about 7 x 7 km in NE Siberia. The approach can be also potentially transferred to medium-resolution C-band SAR data such as ENVISAT ASAR Wide Swath with similar to 120m resolution but it is in general limited to regions without woody vegetation. Global Monitoring-mode-derived SOC increases with unfrozen period length. This indicates the importance of this parameter for modelling of the spatial distribution of soil organic carbon storage.
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| 5. |
- Chadburn, Sarah E., et al.
(författare)
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Carbon stocks and fluxes in the high latitudes : using site-level data to evaluate Earth system models
- 2017
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 14:22, s. 5143-5169
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Tidskriftsartikel (refereegranskat)abstract
- It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France). We use a site-level approach in which comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow. We show that if the models simulate the correct leaf area index (LAI), the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with a similar LAI. The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our analysis suggests that an improved simulation of photosynthesis would also lead to an improved simulation of soil carbon stocks. However, the stocks are also influenced by soil carbon burial (e.g. through cryoturbation) and the rate of heterotrophic respiration, which depends on the soil physical state. More detailed below-ground measurements are needed to fully evaluate biological and physical soil processes. Furthermore, even if these processes are well modelled, the soil carbon profiles cannot resemble peat layers as peat accumulation processes are not represented in the models. Thus, we identify three priority areas for model development: (1) dynamic vegetation including (a) climate and (b) nutrient limitation effects; (2) adding moss as a plant functional type; and an (3) improved vertical profile of soil carbon including peat processes.
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| 6. |
- Faucherre, Samuel, et al.
(författare)
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Short and Long-Term Controls on Active Layer and Permafrost Carbon Turnover Across the Arctic
- 2018
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 123:2, s. 372-390
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Tidskriftsartikel (refereegranskat)abstract
- Decomposition of soil organic matter (SOM) in permafrost terrain and the production of greenhouse gases is a key factor for understanding climate change-carbon feedbacks. Previous studies have shown that SOM decomposition is mostly controlled by soil temperature, soil moisture, and carbon-nitrogen ratio (C:N). However, focus has generally been on site-specific processes and little is known about variations in the controls on SOM decomposition across Arctic sites. For assessing SOM decomposition, we retrieved 241 samples from 101 soil profiles across three contrasting Arctic regions and incubated them in the laboratory under aerobic conditions. We assessed soil carbon losses (Closs) five times during a 1 year incubation. The incubated material consisted of near-surface active layer (ALNS), subsurface active layer (ALSS), peat, and permafrost samples. Samples were analyzed for carbon, nitrogen, water content, δ13C, δ15N, and dry bulk density (DBD). While no significant differences were observed between total ALSS and permafrost Closs over 1 year incubation (2.3 ± 2.4% and 2.5 ± 1.5% Closs, respectively), ALNS samples showed higher Closs (7.9 ± 4.2%). DBD was the best explanatory parameter for active layer Closs across sites. Additionally, results of permafrost samples show that C:N ratio can be used to characterize initial Closs between sites. This data set on the influence of abiotic parameter on microbial SOM decomposition can improve model simulations of Arctic soil CO2 production by providing representative mean values of CO2 production rates and identifying standard parameters or proxies for upscaling potential CO2 production from site to regional scales.
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| 7. |
- Fuchs, Matthias, et al.
(författare)
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Low below-ground organic carbon storage in a subarctic Alpine permafrost environment
- 2015
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 9:2, s. 427-438
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the soil organic carbon (SOC) storage in Tarfala Valley, northern Sweden. Field inventories, upscaled based on land cover, show that this alpine permafrost environment does not store large amounts of SOC, with an estimate mean of 0.9 +/- 0.2 kg C m(-2) for the upper meter of soil. This is 1 to 2 orders of magnitude lower than what has been reported for lowland permafrost terrain. The SOC storage varies for different land cover classes and ranges from 0.05 kg C m(-2) for stone-dominated to 8.4 kg C m(-2) for grass-dominated areas. No signs of organic matter burial through cryoturbation or slope processes were found, and radiocarbon-dated SOC is generally of recent origin (< 2000 cal yr BP). An inventory of permafrost distribution in Tarfala Valley, based on the bottom temperature of snow measurements and a logistic regression model, showed that at an altitude where permafrost is probable the SOC storage is very low. In the high-altitude permafrost zones (above 1500 m), soils store only ca. 0.1 kg C m(-2). Under future climate warming, an upward shift of vegetation zones may lead to a net ecosystem C uptake from increased biomass and soil development. As a consequence, alpine permafrost environments could act as a net carbon sink in the future, as there is no loss of older or deeper SOC from thawing permafrost.
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| 8. |
- Gentsch, N., et al.
(författare)
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Storage and transformation of organic matter fractions in cryoturbated permafrost soils across the Siberian Arctic
- 2015
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 12:14, s. 4525-4542
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Tidskriftsartikel (refereegranskat)abstract
- In permafrost soils, the temperature regime and the resulting cryogenic processes are important determinants of the storage of organic carbon (OC) and its small-scale spatial variability. For cryoturbated soils, there is a lack of research assessing pedon-scale heterogeneity in OC stocks and the transformation of functionally different organic matter (OM) fractions, such as particulate and mineral-associated OM. Therefore, pedons of 28 Turbels were sampled in 5m wide soil trenches across the Siberian Arctic to calculate OC and total nitrogen (TN) stocks based on digital profile mapping. Density fractionation of soil samples was performed to distinguish between particulate OM (light fraction, LF, < 1.6 g cm(-3)), mineral associated OM (heavy fraction, HF, > 1.6 g cm(-3)), and a mobilizable dissolved pool (mobilizable fraction, MoF). Across all investigated soil profiles, the total OC storage was 20.2 +/- 8.0 kgm(-2) (mean +/- SD) to 100 cm soil depth. Fifty-four percent of this OC was located in the horizons of the active layer (annual summer thawing layer), showing evidence of cryoturbation, and another 35% was present in the upper permafrost. The HF-OC dominated the overall OC stocks (55 %), followed by LF-OC (19% in mineral and 13% in organic horizons). During fractionation, approximately 13% of the OC was released as MoF, which likely represents a readily bioavailable OM pool. Cryogenic activity in combination with cold and wet conditions was the principle mechanism through which large OC stocks were sequestered in the subsoil (16.4 +/- 8.1 kgm(-2); all mineral B, C, and permafrost horizons). Approximately 22% of the subsoil OC stock can be attributed to LF material subducted by cryoturbation, whereas migration of soluble OM along freezing gradients appeared to be the principle source of the dominant HF (63 %) in the subsoil. Despite the unfavourable abiotic conditions, low C/N ratios and high delta C-13 values indicated substantial microbial OM transformation in the subsoil, but this was not reflected in altered LF and HF pool sizes. Partial least-squares regression analyses suggest that OC accumulates in the HF fraction due to co-precipitation with multivalent cations (Al, Fe) and association with poorly crystalline iron oxides and clay minerals. Our data show that, across all permafrost pedons, the mineral-associated OM represents the dominant OM fraction, suggesting that the HF-OC is the OM pool in permafrost soils on which changing soil conditions will have the largest impact.
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| 9. |
- Harden, Jennifer W., et al.
(författare)
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Field information links permafrost carbon to physical vulnerabilities of thawing
- 2012
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39, s. L15704-
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Tidskriftsartikel (refereegranskat)abstract
- Deep soil profiles containing permafrost (Gelisols) were characterized for organic carbon (C) and total nitrogen (N) stocks to 3 m depths. Using the Community Climate System Model (CCSM4) we calculate cumulative distributions of active layer thickness (ALT) under current and future climates. The difference in cumulative ALT distributions over time was multiplied by C and N contents of soil horizons in Gelisol suborders to calculate newly thawed C and N. Thawing ranged from 147 PgC with 10 PgN by 2050 (representative concentration pathway RCP scenario 4.5) to 436 PgC with 29 PgN by 2100 (RCP 8.5). Organic horizons that thaw are vulnerable to combustion, and all horizon types are vulnerable to shifts in hydrology and decomposition. The rates and extent of such losses are unknown and can be further constrained by linking field and modelling approaches. These changes have the potential for strong additional loading to our atmosphere, water resources, and ecosystems. Citation: Harden, J. W., et al. (2012), Field information links permafrost carbon to physical vulnerabilities of thawing, Geophys. Res. Lett., 39, L15704, doi: 10.1029/2012GL051958.
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| 10. |
- Hugelius, Gustaf, 1980-, et al.
(författare)
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Characterization of Soil Organic Matter in Permafrost Terrain – landscape scale analyses from the European Russian Arctic
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 1 INTRODUCTIONSoils of high latitude terrestrial ecosystems are considered key components in the global carbon cycle and hold large stores of Soil Organic Carbon (SOC). The absolute and relative sizes of labile and recalcitrant SOC pools in periglacial terrain are mostly unknown (Kuhry et al. in prep.). Such data has important policy relevance because of its impact on climate change.We sampled soils representative of all major land cover and soil types in discontinuous permafrost terrain, European Russian Arctic. We analyzed the bulk soil characteristics including the soil humic fraction to assess the recalcitrance in organic matter quality in down-depth soil profiles.2 METHODSA comprehensive stratified random soil sampling program was carried out in the Seida area during late summer 2008. From these, we selected nine sites considered representative for the landscape. Active layer and permafrost free upland soils were sampled from dug soil pits with fixed volume corers. Peat plateaus were sampled near thermally eroding edges. Permafrost soils were cored using steel pipes hammered into the frozen peat. Permafrost free fens were sampled using fixed volume Russian corers.Radiocarbon dating was used to determine the SOC ages. The soils were analyzed for dry bulk density, elemental content, and stable isotope composition of organic C and N (δ13C, and δ15N). Further, humic acids were extracted, and the degree of humification of SOM assessed based on A600/C and ∆ log K (Ikeya and Watanabe, 2003).3 RESULTSFigure 1 shows soil organic matter (SOM) characteristics in a peat sequence from one of the nine described sites, a raised bog peat plateau.The peatland first developed as a permafrost-free fen during the Holocene Hypsithermal. Permafrost only aggraded in the late Holocene. Anoxic conditions in the fen and permafrost in peat plateau stages reduced decomposition rates and the degree of humification (A600/C) is relatively constant throughout the peat deposit.Botanical origin is a key factor in determining SOM quality, which is clearly reflected in the elemental ratio (C/N) and isotopic composition of C and N. There are sharp shifts in humification, C/N and isotopic composition at the peat/clay interface.REFERENCESIkeya, K. and Watanabe, A., 2003, Direct expression of an index for the degree of humification of humic acids using organic carbon concentration. Soil Science and Plant Nutrition, 49: 47-53.Kuhry, P., Dorrepaal, E., Hugelius G., Schuur, E.A.G. and Tarnocai C., Potential remobilization of permafrost carbon under future global warming. Permafrost and Periglacial Processes, Submitted.
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